A morphine-like factor "enkephalin", identified in this laboratory in bovine brain by competition for opiate receptor binding, consists of two pentapeptides tyr-gly-gly-phe-leu and tyr-gly-gly-phe-met. We propose to evaluate detailed interactions of enkephalins with the opiate receptor both by studying enkephalin influences on (3H)enkephalins. Degradation of (3H)enkephalin will be examined to assess the existence of specifc enkephalin destroying enzymes as well as general peptidases. The biosynthesis of enkephalin will be studied in vivo and in vitro. Efforts will be devoted to raising antibodies to enkephalin and development of a radiommunoassay.